The present invention relates to a tire with radial carcass reinforcement for heavy vehicles, such as trucks and buses. More particularly, it relates to the beads of radial carcass tires, the seats of which are inclined relative to the axis of rotation at an angle α, where 0°≦α≦6°.
Rims of the “heavy-vehicle” type exhibit the peculiarity of having relatively high rim flanges according to the standards in force (TRA, ETRTO, JATMA), and the tires which use such rims are generally tires mounted with an inner tube accompanied by a flap disposed between the inner walls of the two tire beads.
Each bead comprises a bead wire, generally of the “braided” type, around which is anchored by winding a radial carcass reinforcement of metal reinforcement elements. The radial carcass reinforcement has a main, or non-upturned region, and an upturned region. The height of the upturned region, measured relative to the base of the bead, is greater than the height of the rim flange. The upturn is reinforced axially to the outside by an additional reinforcement armature, which may be made of metal or other elements, oriented relative to the circumferential direction at a slight angle, which may be between 5° and 30°. The additional reinforcement armature is wound around the anchoring bead wire and forms two strands: an axially outer stand the end of which is situated radially slightly above the end of the carcass reinforcement upturn and an axially inner strand, the end of which is generally situated below a straight line parallel to the axis of rotation and passing through the crown of the rim flange.
The main purpose of the additional reinforcement armature is to minimize the movement, in the three dimensions, of the radial carcass reinforcement upturn end and the protective layer of rubber mix. A protective layer of rubber mix, also known as a protector, surrounds the surface of the bead, which has to be in contact with the operating rim.
The additional reinforcement armature formed of metal elements or other elements is costly, and much research has been carried out with a view to dispensing with the additional reinforcement armature without thereby affecting the fundamental properties of the tire bead, i.e. ensuring that said tire remains on its operating rim whatever the driving conditions and for the longest possible period, which requires that any solution exhibit excellent properties with regard to endurance and resistance to rim wear.
One solution to the problem of resistance to rim flange wear, resulting from repeated flexure of the tire and movement between beads and rim flanges, is described in patent FR 2,406,530 which provides, for the outer surface of the bead, a suitable meridian profile. The profile consists of a first curved portion, which has to come into and remain in permanent contact with the surface of the rim flange. The first curved portion has at its junction with a second curved portion, an abrupt discontinuity of curvature. The meridian profile of the second curved portion is such that it cannot come into contact with the surface of the rim flange. The discontinuity between two curves may be defined geometrically as being the acute angle, viewed in meridian section, formed by the tangents to the two curves respectively at the junction point. The discontinuity is abrupt if the angle is at least equal to 35°. However, this solution has proven insufficient to compensate for the lack of wear resistance exhibited by the bead, which lack is caused by the absence of an additional bead reinforcement armature.
The object of the present invention is to provide a tire that omits the additional bead reinforcement, armature, while still having suitable bead endurance and resistance to rim wear.